1. Field of the Invention
The present invention relates to an acceleration detecting device of a passive safety system for driving and controlling a passive safety device of a vehicle.
2. Description of Related Art
A conventional acceleration detecting device will be described which is provided in a control unit (passive safety system) for controlling the operation of a passive safety device of a vehicle such as an air bag system or the like.
FIG. 11 is an illustration to show an example of a position where a control unit including a conventional acceleration detecting device and a passive safety device are disposed in a vehicle and to show a view when viewed from the top side of the vehicle. In FIG. 11, a reference character 110 denotes a control unit having the acceleration detecting device disposed in the center tunnel (not shown) of the vehicle. A reference character 111 denotes the passive safety device disposed in a steering wheel (not shown).
FIG. 12 is a side view to show a schematic configuration of the conventional acceleration detecting device. In FIG. 12, a reference character 100 denotes the acceleration detecting device. A reference character 101 denotes a mass body having a mass and a reference character 102 denotes a sliding shaft for slidably supporting the mass body 101. A reference character 103 denotes an elastic body disposed in such a way as to surround the sliding shaft 102. When the acceleration detecting device 100 is not operated, the mass body 101 is pressed onto one side by the elastic force of the elastic body 103. A reference character 104 denotes movable contact points each formed in the shape of a spring and fixed to the top and bottom of the mass body 101. A reference character 105 denotes fixed contact points fixed to the ceiling portion and bottom portion of a tunnel-shaped hole, made in the acceleration detecting device 100, into which the mass body 101 goes when it slides on the sliding shaft 102.
FIGS. 13A and 13B are illustrations of the mass body 101 and the sliding shaft 102 constituting a part of the conventional acceleration detecting device 100. FIG. 13A is a perspective view of the mass body and the sliding shaft in the ordinary state where the acceleration detecting device 100 is not operated and FIG. 13B is a cross-sectional view. In FIG. 13, a reference character 101 denotes the mass body. The mass body 101 is made of brass, for example, and has a predetermined mass. A reference character 101a denotes a through hole made through the mass body 101. A reference character 102 denotes the sliding shaft passing through the through hole 101a and being fixed. The sliding shaft 102 is made of, for example, a PBT (polybutylenephthalate) resin or the like and is circular in cross section. The through hole 101a and the sliding shaft 102 are formed, for example, by a die molding method or the like. The circle of the cross section of the mass body 101 is larger than the circle of the cross section of the sliding shaft 102, so the mass body 101 can slide on the sliding shaft 102. A reference character Gz denotes a gravity component applied to the mass body 101.
In the state where the acceleration detecting device 100 including the mass body 101 and the sliding shaft 102 is not operated (hereinafter referred to as an ordinary state), only the gravity Gz is applied to the mass body 101 and thus the upper portion of the mass body 101 is in contact at one point with the upper portion of the sliding shaft 102.
Next, the operation of the acceleration detecting device 100 will be described.
In the case where a vehicle collides with an object in front of the vehicle and receives an impact (deceleration), the mass body 101 receives an inertial force from the impact. In the case of a large impact, the inertial force overcomes the elastic force of the elastic body 103 to slide the mass body 101 on the sliding shaft 102 to put the mass body 101 into the tunnel-shaped hole. When the mass body 101 moves a distance larger than a predetermined distance, the movable contact points 104 come in contact with the fixed contact points 105 to bring these two contact points into electric conduction.
The acceleration detecting device 100 is a mechanical type device and the control unit 110 has double circuits of the acceleration detecting device 100 and an electromechanical acceleration detecting device (semiconductor acceleration sensor). Only after both the circuits output a signal to operate the passive safety device 111, the passive safety device 111 is operated. The circuits for operating the passive safety device 111 will be described in the following.
FIG. 14 is a circuit diagram to show an electric configuration of the control unit 110 provided with the conventional acceleration detecting device 100 and the passive safety device 111. In FIG. 14, a reference character 112 denotes a power source. A reference character 113 denotes a semiconductor-type acceleration sensor having a function of detecting an impact acceleration applied to the vehicle. A reference character 114 denotes a microcomputer having a function of processing a signal from the semiconductor-type acceleration sensor 113. A reference character 115 denotes a semiconductor switch for opening or closing a driving circuit of the passive safety device 111.
The control unit 110 is constituted by the power source 112, the semiconductor-type acceleration sensor 113, the microcomputer 114, the semiconductor switch 115 and the mechanical acceleration detecting device 100. Further, the passive safety device 111 is constituted by the driving circuit, opened or closed by the semiconductor switch 115, and the safety device body.
Next, the operation of the circuit of the control unit 110 and the passive safety device 111 will be described.
For example, in the case where a vehicle collides head-on with an object, the semiconductor-type acceleration sensor 113 disposed in the control unit 110 detects an impact acceleration and outputs a detected acceleration signal to the microcomputer 114. The microcomputer 114 converts the signal from the semiconductor-type acceleration sensor 113 into digital data by means of an internal A/D converter and performs a predetermined processing to close the semiconductor switch 115 if the impact is larger than a predetermined value.
Further, similarly, in the mechanical acceleration detecting device 100 disposed in the control unit 110, in the case where an impact larger than a predetermined value is applied to the vehicle, as described above, the internal contact points are brought into conduction to close the circuit.
In this manner, when the vehicle receives the impact larger than the predetermined value, both circuits of the semiconductor switch 115 and the mechanical acceleration detecting device 100 are closed to pass a current through the driving circuit of the passive safety device 111, thereby operating the passive safety device 111.
The acceleration detecting device in the conventional passive safety device of the vehicle is constituted in this manner and performs the predetermined operation. However, since both of the mass body 101 and the sliding shaft 102 are circular in cross section, the movement of the mass body 101 becomes unstable, depending on the direction of collision of the vehicle, and when the mass body 101 slides on the sliding shaft 102, the mass body 101 rattles. In this case, there is presented a problem that the timing of operation of the passive safety device might be delayed.
The problem will be described in detail in the following.
In the case where the vehicle collides head-on with the object, the direction of impact applied to the mass body 101 agrees with the direction of detecting an acceleration, that is, the axial direction of the sliding shaft 102. For this reason, the mass body 101 can stably slide on the sliding shaft 102.
Next, the case will be described where the vehicle collides obliquely with the object. FIGS. 15A to 15C are illustrations to show the contact state where the mass body 101 is put into contact with the sliding shaft 102 in the case where the vehicle collides obliquely with the object. FIG. 15A is a perspective view and FIGS. 15B and 15C are cross-sectional views. In FIG. 15A, a reference character Gz denotes a gravity component applied to the mass body 101 and a reference character Gx denotes an impact acceleration component in the direction of the sliding shaft 102. A reference character Gy denotes an impact acceleration component produced in the left and right direction, assuming that the direction of the sliding shaft 102 is the front and rear direction.
In the case where the vehicle collides obliquely with the object, the impact applied to the mass body 101 produces not only an impact acceleration component Gx in the direction of the sliding shaft 102 but also an impact acceleration component Gy in the direction at an angle of 90 degrees with respect to the direction of the Gx on the horizontal plane. In the ordinary state where the acceleration detecting device 100 is not operated, only the gravity Gz is applied to the mass body 101 and thus the mass body 101 comes in contact with the sliding shaft 102 at one point of the upper portion (see FIG. 13B).
However, when the vehicle collides obliquely with the object, the impact acceleration components Gx, Gy in the horizontal direction are larger than the gravity component Gz in the vertical direction, so the mass body 101 moves in the horizontal direction at an angle of 90 degrees with respect to the sliding shaft 102 and comes in contact with the sliding shaft 102 at one point in the left and right direction. A rotational moment is produced by a frictional force, produced by the contact, between the mass body 101 and the sliding shaft 102 to rotate the mass body 101, thereby rattling the mass body 101 when the mass body 101 slides.
FIG. 15C is a cross-sectional view to show the state where the mass body 101 rotates around the sliding shaft 102. As described above, in the case where the rotational moment is produced to rotate the mass body 101, the rotational moment depends on the frictional force and makes the movement of the mass body 101 unstable if the surface conditions of the through hole 101a of the mass body 101 and the sliding shaft 102 are not uniform. Thus, this raises the possibility that the timing of operation of the passive safety device might be delayed.
The present invention has been made to solve the above problems. The object of the present invention is to provide an acceleration detecting device in which a mass body can stably slide on a sliding shaft, irrespective of the direction of an impact.
An acceleration detecting device in accordance with the present invention has a mass body having: a predetermined mass and a through hole made through the mass body; and a sliding shaft passing through the through hole and sliding the mass body, wherein the sliding shaft comes in contact with the through hole at two or more points to support the mass body.
In an acceleration detecting device in accordance with the present invention, when the through hole is circular in cross section, the sliding shaft is formed in such a shape that the sliding shaft comes in contact with the through hole at two or more points to support the mass body.
In an acceleration detecting device in accordance with the present invention, the sliding shaft has a cross section formed in the shape of an oblong circle elongated in the lateral direction.
In an acceleration detecting device in accordance with the present invention, the sliding shaft is provided with a projection for regulating the rotation of the mass body.
In an acceleration detecting device in accordance with the present invention, when the sliding shaft is circular in cross section, the through hole is formed in such a shape that the sliding shaft comes in contact with the through hole at two or more points to support the mass body.
In an acceleration detecting device in accordance with the present invention, the through hole is provided with a plane for regulating the rotation of the mass body.